Valves for controlling the flow of fuel in torches are described, for example, in U.S. Pat. No. 5,123,837 and U.S. Pat. No. 5,176,175. Typically, the primary shut off mechanism of such valves includes a valve needle tip making metal to metal contact with a valve seat formed in the valve body. The needle is threadedly connected to the valve body, and turning the needle advances the needle tip into contact with the valve seat. The last part of the movement which makes positive contact of the needle with the valve seat includes rotation of the needle tip against the valve body. A special lubricant is used on the contact surfaces of the needle and valve seat. Without the lubricant, galling of the surfaces of the valve seat and needle tip could occur. In addition, to ensure that the needle and valve seat form a reliable seal, the machining tolerances of these parts must be tightly controlled, which adds manufacturing expense.
The present invention provides an improved valve that eliminates these problems. A valve according to the present invention includes a valve body having a central, axial bore and a valve needle threadedly mounted in the bore for selectable axial positioning in the bore. A first or inlet portion of the bore includes an inlet connectable to a source of pressurized fuel. A second portion of the bore carries the valve needle. An outlet passage communicates with the bore at a point approximately where the second portion joins the first portion. The outlet passage extends laterally from the bore to open at an outlet orifice on the outer surface of the valve body. The outlet orifice includes means for attaching a torch and igniter assembly to the valve body.
According to the invention, the needle includes a stem that terminates in a needle tip. An annular ridge extends from the stem spaced from the tip and defines a first groove between the ridge and stem. A second groove is formed in the stem spaced from the first groove. Each of the first and second grooves carries a resilient sealing ring. The second groove and ring seal the bore from the ambient environment. By positioning the needle valve with the first groove and ring between the outlet passage and the inlet, the outlet is closed from the inlet. The needle may be moved toward the second end of the valve body to open the outlet passage to the inlet of the bore.
The seal according to the invention relies on contact between the resilient rings and the surface of the bore. The metal to metal contact and wear in conventional valves is thus avoided. Further, the sealing rings are inexpensive and easily replaced, if necessary.
According to another aspect of the invention, the outlet passage communicates with the bore at an outlet coupling portion having a first diameter. A sealing portion of the bore having a second diameter less that the first diameter extends from the outlet coupling portion toward the inlet. The outlet passage opens into the outlet coupling portion adjacent to a junction between the bore portions. In the closed position, the first groove and first resilient ring are positioned in the sealing portion with the ring in sealing engagement with a surface of the sealing portion of the bore.
According to another aspect of the invention, regulation of the pressure of gas in the outlet passage is achieved by a pin and spring arrangement disposed in the inlet portion of the bore. The inlet includes valve seat means. The pin includes a flange extending radially from the pin shaft. In a closed position, the flange engages the valve seat means of the valve body. The spring is disposed between the collar of the needle and the flange and biases the flange into the closed position. The spring force is adjusted according to the position of the needle in the bore, that is, as the needle is moved toward the inlet of the bore, the spring is compressed, thus increasing the spring force. As a result, increased gas pressure is required to overcome the spring force to allow gas to flow past the pin.